Ion source for slow-ion sputtering

ABSTRACT

AN ION SOURCE FOR A SPUTTERING APPARATUS COMPRISING AN OPEN CYLINDER IN WHICH AT ONE END A FILAMENT CATHODE IS ARRANGED, WHICH SCREENED BY TWO SCREENING PLATES AT RIGHT ANGLES TO THE AXIS. AN AXIAL MAGNETIC FIELD IN THE ANODE OF A FEW HUNDRED GAUSS BRINGS ABOUT A LOW BURNING VOLTAGE OF ABOUT 30 TO 40 V.

March 6, 1973 E. F. HANSEN ETAL 3,719,582

ION SOURCE FOR SLOW-ION SPUTTERING Filed om. 15. 1970 I N V E NTORSNORBERT E.F. HANSEN WALTER F.K. LITTMANN AGENT United States Patent3,719,582 ION SOURCE FOR SLOW-ION SPUTTERING Norbert Ernst Fritz Hansen,Roetgen, and Walter Fritz Konrad Littmann, Eildendorf, near Aachen,Germany, asslgnors to US. Philips Corporation, New York, N.Y.

Filed Oct. 15, 1970, Ser. No. 80,972 Claims priority, applicationGermany, Oct. 21, 1969, P 19 53 659.5 Int. Cl. C23c 15/00 US. Cl.204-298 3 Claims ABSTRACT OF THE DISCLOSURE An ion source for asputtering apparatus comprising an open cylinder in which at one end afilament cathode is arranged, which is screened by two screening platesat right angles to the axis. An axial magnetic field in the anode of afew hundred gauss brings about a low burning voltage of about 30 to 40v.

The invention relates to an ion source for slow-ion sputtering, in whichthe ions are produced in a non-selfiiustlained discharge occurring atleast partly in a magnetic In the arrangement disclosed in Britishpatent specification 1,113,579 the filament cathode of the discharge isarranged in the gas supply chamber which communicates through a smallorifice with the sputtering space, where the anode is accommodated. Theanode surrounds the material to be sputtered, the target. The objects tobe sputtered, the substrate, are disposed at the side of the dischargepath around the same. In front of the anode in the discharge space amagnetic field of a few hundred gauss prevails in parallel to thedischarge path.

In this arrangement it is diflicult to act upon the paths of thesputtered particles by magnetic and/or electric agency independently ofthe magnetic field in the discharge path. The anode voltage of thedischarge is stated to be 60 v.

Although this anode voltage seems to be low, ions may nevertheless occurat the low pressures in the discharge, the velocity of said ionsexceeding 50 ev. Such ions release particles from the apparatus, whichresults in that the ready products exhibit contaminations by thesereleased particles.

From the Swiss patent specification 465,996 there is known a sputteringarrangement in which the ions emanating from an ion source are orientedby an axial magnetic field to the sputtering plates. The ions sourcecomprises a magnetic lens for guiding the ions. The filament cathode ofthe ion source is located, however, in a space free of a magnetic field.

The invention has for its object to provide an ion source for slow-ionsputtering, in which only ions having low primary energies are formedand high ion flows are obtained.

In an ion source for slow-ion sputtering, in which the ions are producedin a non-self-sustained discharge occurring at least partly in amagnetic field, the anode is formed, in accordance with the invention,by an open cylindrical sheath accommodating at one end the filamentcathode, while in the discharge path between the anode and the cathodeprevails a magnetic field of a few hundred gauss in an axial directionrelative to the anode. Owing to the relative disposition of the twoelectrodes in the magnetic field a very intensive discharge is producedby anode voltages of at the most 30 to 40 v. at an argon pressure ofabout 10" torr, said discharge being of the order of 10 A. in accordancewith the dimensions. The plasma of this discharge extends from the openend of the anode opposite the cathode in the vacuum space and from thisplasma the ions having primary energies always at the most equal to theanode voltage, i.e. 30 to 40 v. can be directed to the target plates byelectric fields and, if desired, by magnetic fields. The magnetic fieldof the main discharge, which is fairly weak beyond the anode, affectsthe path of the ions and of the sputtering products only to a slightextent. The disposition of the targets and of the substrate maytherefore be rather arbitrary.

In order to protect the sputtering space from evaporation products ofthe cathode, a screening plate at a floating potential is arranged infront of the cathode, viewed in the direction towards the sputteringspace. Also on the other side of the cathode a screening plate isprovided, which is preferably connected with a beaker surrounding theanode. The two screening plates are preferably connected with eachother. The low anode voltage ensures that no uncontrolled sputtering ofthe apparatus occurs, whereas a plasma for the desired sputtering isavailable with high intensity.

The invention will be described more fully with reference to thedrawing, which shows schematically an ion source embodying theinvention.

The filament cathode 1 is arranged at one end of the cylindrical anode 2formed by a copper tube traversed by a coolant; 3 designates a screeningplate, connected by two supporting rods 5 with the second screeningplate 4. The plate 4 holds the copper screening beaker 6. All electrodesare held by through-connections 7 formed by rods or copper tubes, whichare fastened in glass tubes 8 to the supporting plate 9. The supportingplate 9 is secured in flange 10, which is bolted to the flange 11 of thehousing part 12. A magnetic coil 13 surrounds the centre of the anode.At the side of the axis of the anode 2, the target 14 is arranged andopposite the latter the substrate (not shown). An electric screen isdesignated by 15 and an auxiliary magnet by 16.

If an argon pressure of 10- torr prevails in the discharge space and ifthe intensity of the magnetic field is 500 gauss, the discharge currentis 12 A. with an anode voltage of 30 v. The anode 2 has a diameter of 6ems. and a length of 10 cms. The cathode 1 has a heating energy of 250w.

With a target voltage of 300 v., target currents of 20 ma./cm.'- can beattained so that high rates of sputtering can be obtained.

What is claimed is:

1. An ion source for slow-ion sputtering of an object at a given objectposition, comprising an anode formed as a cylindrical sheath, a cathodelocated at one end of the anode, a screening plate located between thecathode and the object position to be sputtered, said screening plateblocking a direct path between said cathode and said object position,said object position being located beyond the other end of the anode,and means for producing a magnetic field, said magnetic field extendingaxially with respect to the anode and being a few hundred gauss in theReferences Cited discharge path between the cathode and the anode.UNITED STATES PATENTS 2. An ion source as claimed in claim 1, furthercomprising a second screening plate opposite the first screen- 3,516,9195/1970 Gaydou et a1 204 2'98 ing plate, said cathode being locatedbetween said first 5 3,408,283 10/1968 Chopra et a1 2O4298 and saidsecond slcrteenting plattesflanctl said tfirstt alnd said FOREIGNPATENTS secon screening p a es emg a a 0a mg po en 1a 3. An ion sourceas claimed in claim 2, further com- 465996 1/1969 Swltzerland 204-298prising a screening cylinder surrounding the anode, said JOHN H MACKPrimary Examiner screening cylinder being fixed in position by saidsecond 10 screening plate, S. S. KANTER, Assistant Examiner

